1. Field of the Invention
The present invention relates to the production of nitrogen solution type fertilizer, which fertilizer solutions are produced by the reaction of phosphoric acid with commercially available nitrogen solutions such as those containing 35 percent urea, 45 percent ammonium nitrate, and 20 percent water. In another embodiment of the present invention, there is taught a method for the production of solutions which contain urea nitrate and ammonium bisulfate by the admixing of sulfuric acid and urea with urea ammonium nitrate solutions. In the first instance of the production of nitrate nitrogen solutions, the typical grade produced thereby is a 27-9-0, whereas, in the second instance and embodiment of the instant invention of production of urea nitrate and ammonium bisulfate solutions, the typical grade produced thereby is 25-0-0-4S.
2. Description of the Prior Art
The production of urea phosphate has been known for over 60 years. Clarkson et al., in U.S. Pat. No. 1,440,056, teach a process for the production of urea phosphate. In their process, urea was reacted with phosphoric acid producing a urea phosphate compound. Other researchers in Germany and Great Britain also produced crystalline urea phosphate. This work was covered under German Pat. No. 2,100,413 and British Pat. No. 1,191,635, respectively. Following is a summary of some of the other researchers who worked with the reaction of urea and phosphoric acid.
A. Gittenait, M., Ger. Offen No. 2,100,413. "Process for the Production of Reaction Products from Phosphoric Acid, Urea and Ammonia and Their Use as Fertilizers," July 15, 1971; PA1 B. Gittenait, M., "Process for Obtaining New Reaction Products of Phosphoric Acid, Urea and Ammonia, and Their Application in the Fertilizer Industry," Paper No. ITE/71/9. Intended for presentation at FAI-ISMA Seminar on Recent Advances in Fertilizer Technology, New Delhi, India, Dec. 6-10, 1971. Gittenait, Marcel, U.S. Pat. No. 3,713,802, Jan. 30, 1973. PA1 C. Keens, D. Ger. Offen. No. 1,912,125, "Urea Phosphate," Oct. 9, 1969; British Appl. Mar. 11, 1968. PA1 D. Koebner, A., Edwards, R. H., and William, T. A., British Pat. No. 1,191,635. "Improvements in Manufacture of Orthophosphates," May 13, 1970. PA1 E. Nayar, K. V., and Gopinath, R. "Manufacture of High-Analysis Complex Fertilizers Through Urea-Phoaphate Route from Wet-Process Acid." Presented at ISMA Technical Conference in Sandefjord, Norway, Sept. 8-11, 1970. PA1 F. Beremzhanov, B. A., and Nurakhmetov, N. N. "Isotherms of Solubility of the System (CO(NH.sub.2).sub.2 --H.sub.3 PO.sub.4 --H.sub.2 O at 0.degree. C. and 10.degree. C." Izv. Akad, Nauk Kaz. SSR, Ser. Khim 18 (2), 43-7 (1968). PA1 G. Kaganskii, I. M. Mukhlya, G. S., Kharlamova, V. M., and Naumov, V. A. "Solubility in the Urea-Phosphate Acid-Water System." Zh. Prikl. Khim. 37 (5), 1111-16 (1964). PA1 (1) Produce a low pH liquid that will not cause germination damage or burned foliage. PA1 (2) Produce a solution-type fertilizer that has a salting-out temperature of less than 50.degree. F. and preferably as low as 0.degree. F. PA1 (3) Use commercially available low-cost materials such as urea, nitrogen solution and wet-process phosphoric acid, which acid has a much lower cost than the superphosphoric acid that is usually used to produce solution-type fertilizers. PA1 (4) Produce N:P, N:PK, N:S, and N:P:K:S solution-type fertilizers by cold mixing NP fertilizers and NS fertilizers with potassium chloride (KCl). PA1 (5) Produce a fertilizer that contains a significant portion of its nitrogen as the desirable nitrate nitrogen. PA1 (6) Produce a solution type fertilizer which has good, prolonged storage characteristics. PA1 (7) Produce low pH solution-type fertilizers in noncomplicated mixing equipment. PA1 (8) Produce solution-type fertilizers that can be stored in stainless steel or plastic tanks. PA1 (9) Produce low price solution-type fertilizers that can be easily and accurately injected beneath the soil. PA1 (10) Produce solution-type fertilizers that contain all three major nutrients (N:P and K) and minor nutrient (S).
Researchers, in more recent times, have also produced solutions from urea and sulfuric acid. See, for example, U.S. Pat. No. 4,116,664, Jones, Sept. 25, 1978, wherein is reacted urea with sulfuric acid to produce solution type fertilizers which have various grades and have a pH of less than 4. These products do not contain nitrate nitrogen. All of the nitrogen is supplied as urea nitrogen which, when applied to the soil, decomposes into ammonium nitrogen. Although the crop does absorb some ammonium nitrogen, it usually absorbs most of its nitrogen as nitrate nitrogen. However, microorganisms will decompose the ammonium nitrogen and convert it to nitrate nitrogen. This reaction requires some time to occur in the soil. The conversion is dependent upon the soil temperature and the quantity of microorganisms. It can occur within several weeks or it may take as long as several months in cool soils. Therefore, there are some advantages to having some nitrate nitrogen available for early response.
A still more recent development is taught in U.S. Pat. No. 4,315,763, Stoller, Feb. 16, 1982, wherein urea is reacted with phosphoric acid or combinations of phosphoric acid and sulfuric acid to produce solution type fertilizers; however, the product therefrom, as is the case in the product of Jones, supra, does not contain the highly desirable form of nitrate nitrogen.
It has been hypothesized that both Jones and Stoller, supra, avoided the use of phosphoric acid with other readily available fertilizer compounds such as urea-ammonium nitrate solution because of the low solubility of the nitrate compounds and the resulting ammonium phosphate solution. This difficulty was observed in our own earlier tests wherein urea-ammonium nitrate solution (45 percent ammonium nitrate, 35 percent urea, and 20 percent water) was reacted with phosphoric acid and a solid gel type substance formed in the fluid which made it impractical for handling and application. However, we discovered that when urea was added along with the conventional urea-ammonium nitrate solution, the result, quite unexpectedly, is a true solution containing highly desirable quick-acting nitrate nitrogen and the slower reacting urea nitrogen.
The production of urea nitrate per se is well known in the art. Urea nitrate (CO{NH.sub.2 }.sub.2.NHO.sub.3) is an additive compound of urea, a very weak base, with HNO.sub.3, a very strong acid. It has a low solubility in nitric acid and a high solubility in water. In the middle 1920s, Lipman and Mehean found it to be an excellent source of nitrogen. Urea nitrate has been made in commercial quantities by BadischeAnilin and Soda Fabrik of Ludwigshafen, Germany. This is a crystalline product and does not contain highly soluble and highly desirable ammonium phosphate (NH.sub.4 H.sub.2 PO.sub.4) as is found in the product produced by practicing the instant invention.
In U.S. Pat. No. 3,713,802, Gittenait, Jan. 30, 1973, there is taught the production of NP and NPK fertilizers by the reaction of phosphoric acid, urea and ammonia to produce various types of solid fertilizer. Although this invention has some merit, its resulting product does not contain the agronomically desirable nitrate nitrogen, whereas, the products resulting from practicing the teachings of the instant invention do contain this type of nitrogen.
Following the teachings of Jones and Stoller, supra, results in the production of solutions containing an adduct CO(NH.sub.2).sub.2.H.sub.3 PO.sub.4 or CO(NH.sub.2).H.sub.2 SO.sub.4 addition compound. Stoller teaches that his solution is a nonammoniated solution, whereas the teachings of the present invention are quite different from that taught by Stoller in that phosphoric acid is caused to be in situ ammoniated. The nitrate portion of the urea ammonium nitrate solution dissociates into ammonium and nitrate ions which, in turn, react with the phosphoric acid to form ammonium phosphate and the nitrate ions react with the urea to form urea nitrate. The reaction proceeds according to the following equation: EQU H.sub.2 O+NH.sub.4 NO.sub.3 +H.sub.3 PO.sub.4 +CO(NH.sub.2).sub.2 .fwdarw.CO(NH.sub.2).sub.2.HNO.sub.3 +NH.sub.4 H.sub.2 PO.sub.4 +H.sub.2 O
In our invention, even though the phosphoric acid is ammoniated, the pH still remains at low values, i.e., between about 0.8 and about 4.5. The resulting mixtures of urea, urea nitrate, and phosphoric acid that are produced by the practice of the instant invention generally have a much lower salt-out temperature than the urea phosphate solutions produced by following the teachings of Stoller, supra. For example, the salt-out temperature of a 27-9-0 grade produced by the present invention is of the order of -5.degree. F. to about 0.degree. F., whereas, the salt-out temperature of a 27-9-0 grade produced by following the dictates of Stoller is about 90.degree. F.
In another series of tests on still another embodiment of the present invention, sulfuric acid was incorporated with urea-ammonium nitrate solution and initially formed a poor quality solution, i.e., one which contained a large amount of solids. However, when additional quantities of urea and sulfuric acid were added to the urea-ammonium nitrate solution, a clear solution was produced. Calculations show that the reaction of additional sulfuric acid with the urea-ammonium nitrate solution and urea formed urea nitrate and ammonium bisulfate. It would be expected that the urea nitrate, which has a low solubility, would crystallize out of the solution; however, test results show that the solubility of the urea nitrate and ammonium bisulfate compounds is high in a solution that has a urea N:ammonium nitrate N mole ratio of 3.5. The product resulting from the practice of the instant invention is substantially different from that obtained by following the teachings of Jones U.S. Pat. No. 4,116,664, supra, in that the H.sub.2 SO.sub.4 added to the urea-ammonium nitrate solution is caused to be ammoniated by the dissociated ammonia from the ammonium nitrate in the urea-ammonium nitrate solution. Therefore, the product resulting in the practice of this embodiment of our invention contains urea nitrogen, nitrate nitrogen, and the secondary element sulfur; it contains the desirable urea nitrate and ammonium bisulfate compounds; its pH varies from about 0.8 to about 4.5; and, of course, it contains the desirable secondary plant nutrient, sulfur. A 25-0-0-4S grade produced by practicing our new invention has a salt-out temperature of 45.degree. F., whereas, a product of this grade produced by practicing the teachings of Jones' art has a salt-out temperature of 53.degree. F.